Wind Turbine Grid Infeed with Switchable Frequency Filtering
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Solution Overview
Problem
Existing wind power installations face delays and limited dynamics in active power reactions to frequency disturbances, leading to frequency oscillations in weakly damped electrical supply grids, and low-pass filters can exacerbate delays during grid faults.
Innovation Solution
A method involving a filtering device with dual low-pass filtering functions, each with different time constants, allows for a fast reaction to frequency events by initially using the faster filter and switching to a slower filter during grid faults to prevent oscillations, while maintaining a stable power feed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a low-pass filter is used to filter frequency changes before determining active power set-point, then frequency oscillations are damped, but the reaction delay increases during grid faults
Solution Approach 1:
The patent applies dynamics by making the filter time constant adjustable rather than fixed. The control system dynamically switches between a first time constant (shorter) for normal operation and a second time constant (longer) for grid fault conditions. This allows the system to optimize its response characteristics based on real-time grid conditions, achieving both fast reaction and oscillation damping as needed.
Solution Approach 2:
The patent changes the parameter of the low-pass filter (time constant) based on operating conditions. By detecting grid fault conditions and adjusting the filter time constant accordingly, the system transitions between different filtering behaviors to balance the trade-off between reaction speed and oscillation damping, resolving the technical contradiction.
2Measurement precision
If a discrete Fourier transform is used to determine frequency, then frequency measurement is achieved, but delays occur in the active power reaction
Solution Approach 1:
The patent introduces dynamic adjustment of the filter time constant that responds to grid conditions. During normal operation, the shorter time constant allows faster response to frequency changes. During grid faults, the longer time constant prevents oscillation excitation. This dynamic behavior resolves the contradiction between measurement precision and reaction speed.
Solution Approach 2:
The patent applies preliminary action by pre-configuring two different time constants for anticipated operating conditions. The system prepares both filtering characteristics in advance and selects the appropriate one based on detected grid conditions, avoiding the need for complex real-time optimization while achieving both fast response and stability.
3Reliability
If grid-tracking infeed technologies are used to support frequency stability, then frequency-dependent active power control is achieved, but frequency oscillations occur in weakly damped grids
Solution Approach 1:
The patent makes the filter time constant dynamic rather than fixed. By switching between shorter and longer time constants based on grid conditions, the system can provide frequency support when needed while preventing oscillation excitation in weakly damped grids, thus resolving the contradiction between reliability and stability.
Solution Approach 2:
The patent changes the filter parameter (time constant) based on detected grid conditions. This parameter adaptation allows the frequency-dependent active power control to function effectively while avoiding oscillation excitation, resolving the technical contradiction between providing frequency support and maintaining grid stability.
Data Source
AI summary
The disclosure relates to a method for feeding electric power into an electrical supply grid having a mains voltage with a mains frequency using an infeed unit. The method comprises detecting the mains frequency and forwarding the detected mains frequency as frequency measurement signal, filtering the frequency measurement signal into a frequency filter signal by means of a filtering device with low-pass behaviour, determining a frequency-dependent set-point power portion depending on the frequency filter signal, and feeding in electric power depending on the frequency-dependent set-point power portion, wherein to filter the frequency measurement signal by means of the filtering device with low-pass behaviour, at least one first and one second filtering function with low-pass behaviour with characteristic first or second low-pass time constants are used, and the first and second filtering function are entirely or partially interchangeable using at least one of a first or second weighting factor.